WingsWaterAndWheels wrote:
I don’t know the 400, but most airplane flies a lot slower once upside down !!!!
Not everything has inverted fuel/oil systems to cope with an extended inverted flight 
aart wrote:
A combination of 1 and 2 works too of course.
What about adding 3. flying in the wake turbulence of the PA28 in front?
The slowest the PA28 goes the more poser you need on C400, so the whole formation has a natural tendency to stay tight, tough abit inspired from swapping luggage load
That kind of limitation is not unknown; for example my IO540-C4 has one here (note the shaded area) but that one is torque (MP is a proxy for torque) related.
To have a straight min figure for RPM is curious and I bet very few people know that. Mind you, they do say “CMI will continue to evaluate any counterweight releases reported to CMI in an attempt to establish a root cause, including any possible connection with power settings.”
Also: how many decades have these engines been around?
Also I am surprised there is a possible physical process which would de-tune the counterweights below 2300rpm and which would take any significant time to do it; if there was an issue then it ought to take place within a fraction of a second.
It is also interesting because it removes a key option for getting more MPG: fly LOP and with a low rpm.
